The invention relates to a process and device for producing a three-dimensional object by means of sintering by layer-wise solidification of a pulverulent material by sintering of the material at points corresponding to the cross-section of the object by means of the action of radiation energy.
Such a process or such a device are known from European application 0 764 079. The laser-sintering device described there has radiant heaters for pre-heating the sintering powder. The heating capacity of the radiant heaters can be regulated in order to pre-heat the powder to a preset temperature.
A laser-sintering device and a laser-sintering process, in which device or in which process the surface temperature of the powder is measured in the laser focus and as a function thereof the laser power is regulated so that the temperature in the focus remains constant, is known from U.S. Pat. No. 6,153,142.
Pre-heating or pre-warming of powder newly applied to a layer up to a working temperature TA, which lies slightly below the melting point for partly crystalline thermoplastics or up to slightly below the glass transition temperature for amorphous thermoplastics, is carried out to save laser energy and to facilitate a continuous building process. The working temperature TA to be selected depends not only on the type of thermoplastic and may not simply be determined from the theoretical melting or glass transition points. Rather, a series of further material and plant factors are to be taken into account. Hence, in practice charge-related differences of the melting or glass transition point may occur. Furthermore, environmental influences may affect the transition points, for example aging of the powder or influence of moisture. For example mixtures of charges of the same material having variable composition are also used, in particular mixtures of new and used powders, that is unsolidified powder from earlier building processes.
In the known laser-sintering devices and processes, the working temperature and also the required laser power is set according to empirical values for the particular powder or on the basis of tests for each building process. Adaptation to certain powder properties, such as for example adaptation to whether it is new powder, recycling powder, mixtures of powders, is only possible due to pre-tests. The use of empirical values is open to error, the undertaking of tests time and cost intensive.